1. Field of the Invention
The present invention relates to a technique which enables supply of power between apparatuses in, for example, a daisy chain connection via a transmission line.
2. Description of the Related Art
Conventionally, operation power of electrical apparatuses use alternate current (AC) power supplied from an outlet, which is then converted into direct current (DC) power by an AC adapter (AC-DC adapter) outside of each of the apparatuses or by an AC-DC converter circuit in each of the apparatuses. Further, if the supply of AC power is stopped due to a power failure or an instantaneous power interruption, the operation of the apparatus can be continued by using a system that switches the supply of power to a backup power supply (uninterruptible power supply system: UPS).
Japanese Patent Application Laid-Open No. 63-261407 discusses a method for continuously supplying high power to a system having a plurality of power supplying apparatuses. According to this method, when a power supply voltage of one of the power supplying apparatuses that supplies power to the system drops, a semiconductor switch is turned on, and power is supplied from a different power supplying apparatus that can supply power of a higher voltage.
However, the method discussed in Japanese Patent Application Laid-Open No. 63-261407 is a power switching method in which power is supplied to one apparatus from a plurality of power supplying apparatuses, and thus does not describe supply of power between a plurality of apparatuses in a system where the apparatuses are connected via a cable or the like. Considering a system where alternating current power is supplied from one apparatus to another for operation, a voltage drop of the alternating current power may occur depending on a length of the transmission. If the voltage drop occurs, in some cases, a predetermined voltage value may fail to be satisfied, thus resulting in an inoperative condition of the system.
Further, in a system where apparatuses are in a daisy chain connection and where power is supplied from a first AC power supply, a power receiving apparatus downstream of a power receiving apparatus connected to the first AC power supply can also receive power from a second AC power supply connected to the power receiving apparatus. However, due to high resistance in the power receiving apparatus, which is connected to the second AC power supply, voltage drop may be increased. In such a case, the voltage of the second AC power supply may drop, and operation of the downstream apparatuses may become unstable.